1-) identify the substance that most capable of conducting electricity. A) water

ID: 515734 • Letter: 1

Question

1-) identify the substance that most capable of conducting electricity.

A) water
B) solid NaCl
C) sugar dissolved in water
D) NaCl dissolved in water
E) solid sugar

2-) use the data given below to construct a Born- Harber cycle to determine the electron affinity of Br.

k (s) --> K (g) = 89
k (g) --> k+ (g) +e- = 419
Br2 (g) --> 2Br (g) = 193
K (s) + 1/2 Br (g) --> KBr (s) = -394
KBr (s) --> K+ (g) + Br- (g) = 674

A) +246 KJ mol^-1
B) -325 KJ mol^-1
C) +367 kJ mol^-1
D) -885 KJ mol^-1
E) -464 KJ mol^-1

(1) (D) NaCl dissolved in water.

When NaCl is dissolved in water it undergoes complete dissociation to form Na+ and Cl- ions which are responsible to conduct electricity.

NaCl (aq.) -----------> Na+ (aq.) + Cl- (aq.)

(2)

Total enthalpy change = sublimation energy of K + ionisation energy of K + dissociatio energy Of Br2 + Electron affinity of Br + lattice energy

- 394 = + 89 + 419 + (193/2) + electron affinity of Br + (-674)

Electron affinity of Br = - 325 kJ/mol

(B)

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